From 04460639bc75ffcb9ebf90efe6feccc444525b28 Mon Sep 17 00:00:00 2001
From: bculkin2442 <bjculkin@mix.wvu.edu>
Date: Sun, 27 Mar 2016 16:29:12 -0400
Subject: Modified tree constructor to support "special" operators

The use case this was created for was to support unary operators, but
it should support operators of any arities, as well some basic meta
operations. I can't think of any obvious ones off the top of my head
but the potential is there.
---
 .../bjc/utils/parserutils/TreeConstructor.java     | 46 ++++++++++++++++++++--
 1 file changed, 42 insertions(+), 4 deletions(-)

(limited to 'BJC-Utils2/src/main/java/bjc')

diff --git a/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java b/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
index 30c147e..6339d8c 100644
--- a/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
+++ b/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
@@ -2,6 +2,7 @@ package bjc.utils.parserutils;
 
 import java.util.Deque;
 import java.util.LinkedList;
+import java.util.function.Function;
 import java.util.function.Predicate;
 
 import bjc.utils.data.GenHolder;
@@ -28,9 +29,42 @@ public class TreeConstructor {
 	 *            The predicate to use to determine if something is a
 	 *            operator
 	 * @return A AST from the expression
+	 * 
+	 * @deprecated Use
+	 *             {@link TreeConstructor#constructTree(FunctionalList, Predicate, Predicate, Function)}
+	 *             instead
 	 */
 	public static <T> AST<T> constructTree(FunctionalList<T> toks,
 			Predicate<T> opPredicate) {
+		return constructTree(toks, opPredicate, (op) -> false, null);
+	}
+
+	/**
+	 * Construct a tree from a list of tokens in postfix notation
+	 * 
+	 * Only binary operators are accepted.
+	 * 
+	 * @param <T>
+	 *            The elements of the parse tree
+	 * @param toks
+	 *            The list of tokens to build a tree from
+	 * @param opPredicate
+	 *            The predicate to use to determine if something is a
+	 *            operator
+	 * @param isSpecialOp
+	 *            The predicate to use to determine if an operator needs
+	 *            special handling
+	 * @param handleSpecialOp
+	 *            The function to use to handle special case operators
+	 * @return A AST from the expression
+	 * 
+	 *         FIXME The handleSpecialOp function seems like an ugly
+	 *         interface. Maybe there's a better way to express how that
+	 *         works
+	 */
+	public static <T> AST<T> constructTree(FunctionalList<T> toks,
+			Predicate<T> opPredicate, Predicate<T> isSpecialOp,
+			Function<Deque<AST<T>>, AST<T>> handleSpecialOp) {
 		GenHolder<Pair<Deque<AST<T>>, AST<T>>> initState =
 				new GenHolder<>(new Pair<>(new LinkedList<>(), null));
 
@@ -40,13 +74,17 @@ public class TreeConstructor {
 					Deque<AST<T>> lft = par.merge((deq, ast) -> deq);
 
 					AST<T> mergedAST = par.merge((deq, ast) -> {
-						AST<T> right = deq.pop();
-						AST<T> left = deq.pop();
+						AST<T> newAST;
 
-						AST<T> newAST = new AST<>(ele, left, right);
+						if (isSpecialOp.test(ele)) {
+							newAST = handleSpecialOp.apply(deq);
+						} else {
+							AST<T> right = deq.pop();
+							AST<T> left = deq.pop();
+							newAST = new AST<>(ele, left, right);
+						}
 
 						deq.push(newAST);
-
 						return newAST;
 					});
 
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